This invention relates to a focus detection device and an image pick-up device.
A focus detection device is known in which a pupil of a shooting optical system is divided by a plurality of pairs of re-imaging lenses whose intervals (between-axis distance) of apertures of pairs of re-imaging lenses are different, relative image shift amounts are respectively calculated for a plurality of pairs of images formed by light beams whose pupils have been divided, and a true defocus amount is obtained by eliminating a false focus from a plurality of defocus amounts. See, for example, Japanese Patent No. 2910102.